This measurement of the Plank constant on the latest NIST Watt balance, NIST-4, is consistent with watt balance measurements from other countries, and the uncertainty of measurement is actually lower than expected.[4] Says NIST physicist, Stephan Schlamminger, "This measurement was essentially a dry run... We were hoping to achieve an uncertainty of within 200 parts per billion by this point, but we got better fast."[4]

For standard application, the results of three experiments must result in a relative uncertainty of not more than 50 parts per billion, with at least one experiment having less than 20 parts per billion, and all in agreement at a 95% statistical confidence level. The results must also match those of an alternative, but more expensive, method of "counting" atoms in an ultra-pure sphere of silicon.[4] The "counting" is done through an xray diffraction measurement of the atomic spacing.